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nerakboo avatar image
nerakboo asked

MPPT 75/15 stuck in bulk charge mode?

We have this charge controller fitted in our Moho with 120w panel and 2 new Varta LFD 90 leisure batteries. Got the Moho out of covered storage ( so nothing for the MPPT unit to do there) and had 2 new batteries installed, put on hook up and put solar fuse back in. By the next day the batteries were boiling! Nice sunny day but the Mppt unit seemed stuck in bulk charge mode ( fast flashing amber light) with fast flashing green light also. Immediately pulled the 15amp fuse on the solar and the boiling stopped. Seems fine on mains hook up so don't think it's an issue with the Electroblock. Both batteries have been tested and are good so it's not a battery problem. Any ideas?

MPPT Controllersbattery charging
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JohnC avatar image
JohnC answered ·

Hi N. Those are flooded batts, aren't they? They will always 'bubble' somewhat under full charge, so that in itself isn't a concern. Did you measure the Voltage at the time?

**Edit/: I won't delete this cos it's relevant to the discussion below. Italics hereforth ain't gospel.** "If it's high, like above 15V, then it's possible that it's picked up the batts as 24V, and is targetting that profile. Pull the solar and batt wires from it (not just fuses etc), go have a cuppa coffee, reinstate the batt cables first, then the pv, It should now work to 12V (if indeed you're using 12V, you didn't say)."

But yeh, you really must measure V in whatever way you can, before reading anything more sinister into it.

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nerakboo avatar image nerakboo commented ·

Hi John

Thanks for your comments. This wasn’t a gentle fizz, but a raging boil with enough gassing of hydrogen to set off the CO monitor in the van (that was our first indication of an issue). I’m not a fan of explosions!

Did not measure the voltage at the time but do know that the batteries were already fully charged, so should not have been bulk charging anyway. Interestingly have since got the old AGM battery refitted which was still good and we are still stuck in bulk charge mode permanently with fast flashing Amber and green lights even when battery charged up.

I’m not happy to start pulling wires out of the MPPT unit as I’m no technician and it is in a right awkward place. Might be a long trip back to the installers I think.

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Mark avatar image Mark ♦♦ commented ·

Hi @JohnC, I believe that the battery voltage auto detect is purposely setup to only work on the first power up.

The unit then stores the detected battery voltage permanently, unless reset to factory default (in which case it will auto detect on the next power up) or it can be changed at any time using Victron Connect.

I think the initial configuration was to auto detect on every/any power up but this caused issues, so it was later corrected to be a one time event.

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